Recently, self-management of blood pressure is increasingly regarded as important, and a domestic use sphygmomanometer is widely used. In time of measuring the blood pressure, an arm band in which an air bladder is incorporated is wound around part of a living body, and the air is fed into the air bladder so as to pressurize the air bladder. The blood pressure is measured from artery information obtained by compressing the living body. An air pump is used for pressurizing the air bladder. The air pump is provided with a rubber diaphragm forming a pump chamber in a case, and performs a pump operation by a capacity change of the diaphragm. Check valves are installed in the air pump so that the discharged air and the suctioned air do not flow reversely to each other. A thin-film shape rubber material is generally used as the check valves.
The thin-film shape valve serving as a discharge valve has a structure in which the valve is opened by discharge pressure so as to feed the air into an adjacent air chamber, and the valve is closed in time of suctioning the air so that the air is not returned in the reverse direction. The thin-film shape valve serving as a suction valve has a structure in which the valve is opened by suction pressure (minus) so as to suction the air into the pump chamber, and the valve is closed in time of compressing so that the air is not leaked. In general, a shape of the thin-film shape valves includes a cylindrical shape, a thin-film leaf shape, and an umbrella shape. Conventionally, there are various technologies proposed for a thin-film shape check valve and a pump using the check valve (for example, refer to Japanese Unexamined Patent Publication No. 10-131862 (patent document 1), Japanese Unexamined Patent Publication No. 11-218244 (patent document 2), Japanese Unexamined Patent Publication No. 2003-139258 (patent document 3), Japanese Unexamined Patent Publication No. 2002-5029 (patent document 4), and Japanese Unexamined Patent Publication No. 2003-269337 (patent document 5)).
In a small pump described in Japanese Unexamined Patent Publication No. 10-131862 (patent document 1), a cylindrical discharge valve is provided in a center part between a plurality of diaphragms, and suction valves are respectively provided for the diaphragms, so that the central cylindrical valve is sealed in a taper shape to prevent air leakage. A discharge valve and a suction valve described in Japanese Unexamined Patent Publication No. 11-218244 (patent document 2) are formed into an umbrella shape, and ribs are provided in an outer circumference so as to prevent the air leakage from film ends. In a check valve described in Japanese Unexamined Patent Publication No. 2003-139258 (patent document 3), convex portions or concave portions are provided in a discharge valve and a suction valve and fitted to each other, so that positioning is performed and liftup is prevented to prevent the air leakage.
In a small pump described in Japanese Unexamined Patent Publication No. 2002-5029 (patent document 4), a suction hole is formed in a drive body connected to a bottom part of a diaphragm, and a thin-film shape suction valve is provided in the bottom part of the diaphragm. In a diaphragm pump described in Japanese Unexamined Patent Publication No. 2003-269337 (patent document 5), a suction valve is formed into a thin-film shape or a leaf shape, a plurality of the suction valves and a plurality of diaphragms are integrated, and convex portions surrounding suction ports are provided on lower surfaces of the suction valves so as to prevent the air leakage.    Patent Document 1: Japanese Unexamined Patent Publication No. 10-131862    Patent Document 2: Japanese Unexamined Patent Publication No. 11-218244    Patent Document 3: Japanese Unexamined Patent Publication No. 2003-139258    Patent Document 4: Japanese Unexamined Patent Publication No. 2002-5029    Patent Document 5: Japanese Unexamined Patent Publication No. 2003-269337